1. Field of the Invention
The present invention relates to a motor control device for controlling a control object, that is, a motor, such that the operation speed reaches a target value, and more specifically to a motor vibration control device for suppressing the torsional vibration in controlling the operation speed.
2. Description of the Related Art
Setting a motor at a predetermined operation speed can be performed by detecting the actual operation speed of the motor and controlling the electric power provided for the motor based on the difference between the predetermined operation speed and the detected operation speed.
However, since the phase of the loop transfer function of a control system is delayed, the torsional vibration can be generated at a loaded equipment connected to the shaft of a motor.
FIG. 1 is a block diagram showing the configuration of the conventional vibration control device of a motor.
In FIG. 1, a motor 105 is equipped with a control device 100, a power converting unit 103, a current detecting unit 104, a speed detecting unit 106, etc. It transfers the power to a loaded equipment 107 by driving the motor 105 by an output from the control device 100 at a variable speed through the power converting unit 103. In this configuration, the control device 100 is equipped with a speed adjusting unit 101, a current adjusting unit 102, an observer (state observing unit) 109 for estimating the speed and the shaft torque of the loaded equipment system, a weight adder 110, and a torque calculator 108 for calculating a driving torque according to a current value from the current adjusting unit 102.
The speed adjusting unit 101 outputs a driving torque reference .tau..sub.a * to set to 0 the difference between a speed reference .omega..sub.M * and the actual operation speed .omega..sub.M of the motor 105 output by the speed detecting unit 106. The driving torque reference .tau..sub.a * is output as a current value, added by an adder 111 to the current value output by the weight adder 110, and input to the current adjusting unit 102. The current adjusting unit 102 controls the electric current such that the difference between the current value obtained by the above mentioned addition and the current value Id detected by the current detecting unit 104 and actually input to the motor 105 can be set to 0. It outputs a power converting unit control signal Cp to the power converting unit 103. The power converting unit 103 provides an electric power for the motor 105 according to the power converting unit control signal Cp from the current adjusting unit 102.
If the driving torque reference .tau..sub.a * is input to the current adjusting unit 102 without being added to the output of the weight adder 110, then formed is a control circuit of the speed adjusting unit 101, current adjusting unit 102, power converting unit 103, current detecting unit 104, motor 105, speed detecting unit 106, and then back to the speed adjusting unit 101. If the phase of the loop transfer function of the control system is delayed by 180.degree. or more, a torsional vibration occurs. The phase delay must be reduced to suppress the torsion vibration. Thus, in a 2-mass system, for example, the observer 109 outputs to the weight adder 110 the estimated shaft torque .tau..sub.s and load speed .omega..sub.L. The weight adder 110 performs the equation g.sub.1 .tau..sub.s +g.sub.2 .omega..sub.L (g.sub.1 and g.sub.2 represent respective gains), and calculates the current value to be added to the driving torque reference .tau..sub.a *. Therefore, the phase of the loop transfer function of the control system can be advanced by adding the output of the weight adder 110 to the driving torque reference .tau..sub.a *.
The observer 109 is structured according to the algorithm of, for example, Mr. Gopinath based on the equation model representing a complicated mechanical system. That is, in this system, the state variables such as a shaft torque .tau..sub.s, load speed .omega..sub.L, etc. are added through the weight adder 110 to the driving torque reference .tau..sub.a * output by the speed adjusting unit 101, thereby suppressing the torsional vibration of the mechanical system.
The observer 109 is derived from the equation model of the mechanical system and the degree of the transfer function is equal to or higher than the mechanical system in principle. Therefore, the more complicated the mechanical system gets, the more complicated its structure also becomes. Thus, it becomes more difficult to realize the system and adjust its operations. For example, the observer of a 2 mass mechanical system is equipped with 3 integrators, and the observer of a 3 mass mechanical system is equipped with 5 or more integrators. Since the observer is the optimum solution when the structure of the mechanical system is well known, the characteristics are degraded if there arise changes in parameter or structure of the mechanical system, thereby possibly causing the problem that a desired control characteristic cannot be guaranteed.
Accordingly, the present invention aims to successfully control the torsional vibration in a simple structure regardless of a complicated loading mechanical system.